Method and device for predicting the starting ability of a vehicle

ABSTRACT

A device for predicting the starting ability of a vehicle having an internal combustion engine and a starter which is supplied with electrical power by a vehicle battery. The starting ability of the vehicle can be determined particularly easily when a starting current characteristics map is stored in a device of the prediction system from which a starting current is determined under consideration of the state of charge of the battery after a predefined time period and the starting ability of the vehicle is determined from this via a prediction device.

FIELD OF THE INVENTION

The present invention relates to a device and method for predicting thestarting ability of a vehicle.

BACKGROUND INFORMATION

Due to the increasing number of silent consumers such as the IR receiverof the central locking system, anti-theft device, sensors, etc.,vehicles have substantial power consumption, even when shut off. Thereis the risk that a shut-off vehicle may no longer be able to be startedafter a prolonged standstill. Therefore, devices indicating the startingability are used to inform the driver.

A device for predicting the starting ability of a vehicle indicates howlong a vehicle may be shut off until the vehicle battery is dischargedto a point that the vehicle is just able to be restarted or whether astart is still possible after a predefined time has elapsed. Thestarting ability of a vehicle is normally assumed when the battery isable to provide a predefined electric starting power without fallingshort of a set minimum terminal voltage.

German Patent Application No. DE 197 05 634, for example, describesdetermining the starting ability of a vehicle at a predefined startingcurrent and a given starting temperature by calculating the terminalvoltage of the battery during a starting operation. The terminal voltageis calculated from the no-load voltage and the internal resistance ofthe starter battery. The starting current is measured during thestarting operation. A prediction about a future starting ability of avehicle is not possible. In addition, it is relatively complex tomeasure the starting current of the battery during a starting operation.

A method for determining the starting ability of a vehicle is describedin German Patent Application No. DE 1056970 in which an average voltagedrop in the battery is calculated during a starting phase and it isdetermined whether or not a minimum terminal voltage of the battery wasnot met. This method also places high demands on the sensor formeasuring the battery voltage and additionally requires constantcalculation of the battery behavior during a starting operation.Moreover, a prediction about the future starting ability of a vehicle isnot possible.

SUMMARY

An object of the present invention is to provide a device and a methodfor predicting the future starting ability of a vehicle in whichabsolutely no measurements of starting currents or voltages of thevehicle battery are necessary.

In accordance with the present invention, the future starting ability ofa vehicle is determined not on the basis of measured starting currentsor voltages, but rather, the starting ability of the vehicle isdetermined based on a characteristics map (composed of one or multiplecharacteristic curves) of an electrical battery variable such as thestarting current. For this purpose, a characteristics map, in which thedependency of an electrical battery variable, e.g., the starting currentflowing through the starter, on a second battery variable, e.g., thestate of charge SOC of the battery, is represented, is stored in thedevice for predicting the starting ability. The value of the firstelectrical battery variable present during a future starting operation,e.g., a starting current value, may be easily read out from thecharacteristics map when the future second battery variable, e.g., thefuture state of charge (SOCnew), is known. The value read out from thecharacteristics map is a measure of the starting ability of the vehicleat the future starting instant. This method has the advantage thatabsolutely no starting currents or voltages have to be measured duringthe start in order to determine the starting ability.

The characteristics map of the electrical battery variable may bedetermined for a predefined battery type and a predefined startingsystem via measurements on the test bench. The empirically determinedcharacteristics map subsequently has only to be stored in the predictionsystem, so that the anticipated value of the first electrical batteryvariable, such as the future battery current or battery voltage, may bedetermined. As a function of the second battery variable, the device inwhich the characteristics map is stored outputs the value of the firstelectrical battery variable which would be present during a futurestarting operation. The output variable of the device is, for example, astarting current or a battery voltage which appears during a futurestarting operation and may be used to determine the starting ability.

According to a preferred example embodiment of the present invention,the device for predicting the starting ability of a vehicle includes abattery state detection device for determining the state of charge (SOC)of the vehicle battery, a device which determines charge (deltaSOC)drawn from the vehicle battery during a predefined shut-off period fromthe discharge current curve in the shut-off vehicle and calculatesremaining state of charge (SOCnew) of the vehicle battery after thepredefined shut-off period, a device for determining a first electricalbattery variable from a stored characteristics map which outputs a valueof the electrical battery variable which would appear during a futurestart, and a prediction device which determines, based on the outputelectrical battery value, whether the vehicle is able to start after thepredefined shut-off period.

The characteristics map may be stored either in the form of a functionor in the form of value pairs. The characteristic curves of thecharacteristics map are preferably current, voltage, or chargecharacteristic curves as a function of the state of charge of thebattery, for example.

Greater prediction accuracy may be achieved if the temperaturedependency of the battery and the starting system is taken into account.In this case, the characteristics map is additionally a function oftemperature T.

The temperature prevailing at a future start may be determined using adevice for temperature prediction, for example. Since it is impossibleto accurately predict the temperature prevailing at the starting instant(the nighttime temperature may substantially differ from the daytimetemperature), an average of already measured temperatures is preferablydetermined over a predefined period. For generating an average, alow-pass filter, situated downstream from the temperature sensor, may beused, for example. The temperature average is preferably taken intoaccount in determining the first electrical battery variable.

A characteristics map of a mechanical variable of the starting system(the starting system includes all driven parts up to the engine), suchas a torque characteristics map as well as an engine torquecharacteristic curve, is preferably stored in the prediction device. Thetorque characteristics map of the starting system is preferably alsodetermined via test bench measurements.

The torque characteristics map of the starting system is a function ofan electrical battery variable, e.g., the state of charge or theinternal resistance of the battery. As a function of the determinedfirst electrical battery variable, the associated torque characteristiccurve is determined from the torque characteristics map underconsideration of at least state of charge SOCnew. The prediction devicemay thus determine the starting ability of the vehicle via a torquecomparison.

The prediction accuracy may be improved again if the temperature istaken into account in determining the starting torque. Thecharacteristic curves of the torque characteristics map of the startingsystem may therefore also be stored as a function of the temperature.

The characteristics map of the first electrical battery variable may beoptionally adapted to the instantaneous state of the starting systemwhich is influenced by different operating variables. Thecharacteristics map of the first electrical battery variable is, asmentioned above, determined via test bench measurements under definedconditions, such as a defined coolant temperature, a defined batteryinternal resistance, a defined state of glow plugs, etc. A change ofthese parameters affects the electrical battery variables, e.g., thestarting current, during a starting operation. The actually occurringstarting current may thus deviate, for example, from the startingcurrent measured on the test bench. The stored characteristics map ofthe electrical battery variable may be adapted to changed operatingconditions in that the starting current is measured during a startingoperation and the characteristics map is adapted accordingly. Using thisadaptation algorithm, aging of the internal combustion engine and ofcomponents of the starting system in particular, as well as battery andoil changes, may be taken into account.

According to a preferred example embodiment, characteristics maps fordifferent starting systems and engines are stored in the predictiondevice. The starting system includes all parts of the vehicle which areimportant for predicting the starting ability, such as, in particular,the transmission, the battery, the starter, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

An example embodiment of the present invention is described in greaterdetail below based on the figures.

FIG. 1 shows a schematic representation of a device for predicting thestarting ability of a vehicle according to an example embodiment of thepresent invention.

FIG. 2 shows a torque characteristics map of the starting system storedin a prediction device for determining the starting ability of thevehicle.

FIG. 3 shows example method steps of a method for predicting thestarting ability of a vehicle.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 shows a schematic representation of a device for predicting thestarting ability of a vehicle. The starting ability of the vehicle isassumed when a vehicle battery 1 is able to provide sufficientelectrical starting power after a predefined shut-off period t_(off) inorder to start the vehicle without falling short of a predefined minimumterminal voltage.

The vehicle battery is drained by different silent consumers during thevehicle's shut-off period. Particularly when the battery is weak, thedriver must be informed whether the vehicle is able to start after apredefined period, e.g., three days. Alternatively, the driver may alsobe informed as to how long the vehicle will still be able to start.

Prediction of the starting ability generally relies on determining afuture state of charge SOCnew which vehicle battery 1 will have afterpredefined shut-off period t_(off) and using future state of chargeSOCnew to determine starting current I_(start), flowing in the starterduring a starting operation, from a starting current characteristics mapstored in a device 3. Based on determined future starting currentI_(start), it is possible to predict whether the vehicle will be able tostart using a prediction device 4.

Using the device for predicting the starting ability, it may optionallyalso be predicted how long the vehicle will still be able to start. Thismay be determined, for example, in that shut-off period t_(off) isincreased until the result is negative.

A characteristics map of the starting current for different states ofcharge SOC of starter battery 1 is stored in device 3 for determining astarting current I_(start). The starting current characteristics map maybe obtained via test bench measurements and subsequent interpolation ofthe measured values or via computer simulation. Starting currentI_(start), anticipated to flow at a future start, may simply be read outfrom the characteristics map when future state of charge SOCnew of thebattery and possibly the future starting temperature are known.Therefore, no measurement of the battery voltage or the battery current(starting current) during a starting operation is necessary forpredicting the starting ability.

Starting current value I_(start) determined from characteristics map 3defines the starting torque generated by the starting system. Givenstarting current value I_(start) is converted into a torque value forpredicting the starting ability of the vehicle. As shown in FIG. 2, atorque characteristics map of starting system M_(startsystem) is storedin prediction device 4. Shown torque characteristic curve 10 againdepends on state of charge SOC or on internal resistance Ri andoptionally also on temperature T of the starting system. This torquecharacteristics map M_(startsystem) is also determined via test benchmeasurements or simulations.

Moreover, prediction device 4 contains an engine torque characteristiccurve 11 which is generally constant. The actually acting startingtorque M at the future starting instant arises at the intersection ofengine torque characteristic curve 11 and torque characteristic curve 10of the starting system (as a function of future state of charge SOCnew).

The starting ability of the vehicle is established when torque M,determined in such a way, is greater than a required minimum torqueM_(min).

During shut-off period t_(off) of the vehicle, current is constantlydrained from the battery by different switched-on silent consumers. Adevice 5, which calculates the drained charge by simply integrating thedischarge current, for example, is provided for calculating the drainedcharge. The discharge current in the shut-off vehicle is preferablymeasured just after the vehicle is shut off. A more accuratedetermination of the drained charge may be achieved when the dischargecurrent is measured at multiple points in time after the vehicle is shutoff.

Instantaneous state of charge SOC of battery 1 is determined by aconventional battery state detection device 2. Corresponding sensors(not shown) provide battery state detection device 2 with batterytemperature T_(Bat), battery voltage U_(Bat), and battery currentI_(Bat) as input variables.

State of charge SOCnew of battery 1, which appears after predefinedshut-off period t_(off), is calculated by subtracting drained chargedeltaSOC from instantaneous charge SOC at subtractor node 9. Subtractor9, as well as other devices of the prediction system, are preferablyimplemented in the form of software and run in a control unit, forexample.

The prediction accuracy may be improved when the starting currentcharacteristic curves are additionally stored as a function of differentstarting temperatures and the starting temperature is taken into accountin the prediction. For this purpose, the prediction system includes atemperature sensor which measures the ambient temperature. The ambienttemperature is supplied to a device 6 for predicting the startingtemperature, device 6 evaluating a starting temperature which isanticipated to prevail at the starting instant. For this purpose, anaverage is preferably formed from multiple temperature values, e.g., thetemperature values of the last several hours. In the simplest case,averaging may take place via a low-pass filter having a large timeconstant and an averaging function.

Device 3 for determining starting current I_(start) preferably includesstarting current characteristic curves for different starting systems,i.e., for different starter, engine, transmission types, etc. Forcalculating the torque demand of the starting system, the displacement,the number of cylinders, the engine type (diesel/gasoline), additionalconsumer currents (e.g., associated with glow plugs), the transmissiontype (stick shift or automatic transmission) with corresponding dragtorque, and the battery type are of importance. Instantaneous parametersP1 . . . Pi of the starting system are supplied to a selection unit 7which selects the starting current characteristic curve appropriate forthe starting system.

As mentioned above, the starting current characteristics map isdetermined via test bench measurements or simulation under definedancillary conditions (ambient temperature, battery type, state of theglow plugs, etc.). These parameters may change during the course ofoperation. If the instantaneous values are not taken into account whendetermining the future starting current, the actually occurring startingcurrent may deviate from starting current I_(start) read out from thecharacteristic curve. Therefore, the characteristics map is preferablyadapted to the instantaneous conditions.

For this purpose, starting current measurements, for example, arecarried out and the starting current characteristics map, for example,is adapted accordingly by displacing the characteristic curves. Providedthat they are known, different parameters Pk . . . Pz (ambienttemperature, battery type, state of the glow plugs, etc.) may optionallyalso be taken into account in order to select the appropriate startingcurrent characteristic curve. In this case, the starting currentcharacteristic curves would be stored as a function of these parameters.Using this adaptation algorithm, the wear and tear in the internalcombustion engine and the starting system, in particular, as well as theaging of the battery and oil changes, may be taken into account.

FIG. 2 shows the determination of the starting ability of the vehicleusing torque characteristic curves.

For determining an operating point M, which appears during a startingoperation, engine torque M_(engine) over speed n and a characteristicsmap of starting system torque M_(startsystem) are stored in predictiondevice 4. The torque of starting system M_(startsystem) is in turn afunction of state of charge SOC, internal resistance Ri of battery 1,and starting temperature T_(start). If state of charge SOC of thebattery is low, torque M_(startsystem), exerted by the starting system,is reduced in the direction of the dashed line which represents thetorque curve at the lowest state of charge SOC needed for a successfulstart.

The characteristics map of starting system torque M_(startsystem) isagain determined via test bench measurements or simulation.

Prediction device 4 determines operating point M from starting currentI_(start) supplied by device 3 under consideration of state of chargeSOCnew of battery 1 and possibly temperature T and internal resistanceRi. Torque M, acting on the engine, occurs at the point where torqueM_(startsystem), exerted by the starting system, is equal to enginetorque M_(engine). If this operating point M is greater than a minimallyrequired torque M_(min), the vehicle is able to start after predefinedshut-off period t_(off).

In order to determine how long the vehicle may be shut off in totalwithout losing its starting ability, predefined shut-off period t_(off)is incrementally increased until operating point M is within predefinedminimum limits M_(min), n_(min). Preceding time value t_(off) thenapproximately reflects the maximum shut-off period.

FIG. 3 shows example steps of a method for predicting the startingability of a vehicle. Instantaneous state of charge SOC of vehiclebattery 1 is determined in a first step 20 via a battery state detectiondevice 2. Charge deltaSOC, which is drained from vehicle battery 1during a predefined time period t_(off) in the shut-off vehicle, isdetermined in step 21 and state of charge SOCnew of vehicle battery 1after predefined time period t_(off) is calculated in step 22. In step23, an electrical battery variable, e.g., future starting currentI_(start) on the basis of calculated future state of charge SOCnew ofvehicle battery 1, is read out from a characteristics map stored indevice 3. Read out starting current value I_(start) is converted into atorque and compared in step 24 to a minimally required torque M_(min) todetermine whether the vehicle is able to start (case J) or not (case N)after predefined time period t_(off). The torque comparison is carriedout in a prediction device 4. The result is displayed in block 25 or 26via a suitable display element.

1. A device for predicting the starting ability of a vehicle having aninternal combustion engine and a starter which is supplied withelectrical power by a vehicle battery, comprising: a battery statedetection device which determines a state of charge of the vehiclebattery; a first device which uses a discharge current curve todetermine a charge drained from the vehicle battery during a predefinedtime period when the vehicle is shut off; a second device whichcalculates the state of charge of the vehicle battery after thepredefined time period; a third device that determines an electricalbattery variable in which a characteristics map of the electricalbattery variable is stored as a function of the state of charge of thevehicle battery, a value of the electrical battery variable, which ispresent after the predefined time period, being read out from thecharacteristics map; a measurement device configured to measure anelectrical variable of the vehicle battery during a starting operation,wherein the measured electrical variable is used to correct the storedcharacteristics map; and a prediction device which uses the read outvalue of the electrical battery variable to determine whether or not thevehicle is able to start after the predefined time period.
 2. The deviceas recited in claim 1, wherein the characteristics map of the electricalbattery variable is one of a current, voltage, or power characteristicsmap.
 3. The device as recited in claim 1, wherein the characteristicsmap of the electrical battery variable is a function of the temperature.4. The device as recited in claim 3, further comprising: a temperatureprediction device to predict a temperature anticipated to prevail afterthe predefined time period, the predicted temperature being taken intoaccount in the determination of the electrical battery variable.
 5. Thedevice as recited in claim 1, wherein a characteristics map of amechanical variable of a starting system is stored in the predictiondevice.
 6. The device as recited in claim 1, wherein a torquecharacteristics map of a starting system and an engine torquecharacteristics curve are stored in the prediction device.
 7. The deviceas recited in claim 6, wherein the engine torque characteristics map ofthe starting system is a function of the state of charge of the vehiclebattery.
 8. The device as recited in claim 6, wherein the torquecharacteristics map of the starting system is a function of thetemperature.
 9. The device as recited in claim 1, wherein characteristiccurves for different starting systems are stored in the third devicethat determines the electrical battery variable.
 10. A method forpredicting the starting ability of a vehicle having an internalcombustion engine and a starter which is supplied with electrical powerby a vehicle battery, the method comprising: determining aninstantaneous state of charge of the vehicle battery via a battery statedetection device; determining a charge drained from the vehicle batteryduring a predefined time period when the vehicle is shut off;calculating the state of charge of the vehicle battery after thepredefined time period; determining an electrical battery variable basedon the calculated state of charge of the vehicle battery from acharacteristics map stored in a device, wherein at least one measuredelectrical variable of the vehicle battery measured during a startingoperation is used to correct the stored characteristics map; anddetermining whether or not the vehicle is able to start after thepredefined time period via a prediction device which determines thestarting ability on the basis of the battery variable determined fromthe characteristics map.
 11. The method as recited in claim 10, furthercomprising: storing a characteristics map for a starting current in thedevice for determining an electrical battery variable as a function ofthe state of charge of the vehicle battery, a starting current, whichoccurs after the predefined time period, being determined from thecharacteristics map.
 12. The method as recited in claim 10, furthercomprising: comparing, by a prediction device, an engine torque and atorque of a starting system in order to determine a torque acting in thefuture.